This invention relates to an automatic control device able to modulate a lighting facility so as to cyclically provide a change of luminosity. The change of luminosity is in a manner that the luminosity increases gradually from a basic luminosity to higher luminosities step by step till it reaches a maximum luminosity, then goes back gradually to the basic luminosity, and then reduces to lower luminosities step by step till it reaches a minimum luminosity, again goes back gradually to the basic luminosity, and so on. That is, the change of luminosity is based on a selected basic luminosity and varies automatically and cyclically with several numbers of slight change of luminosity step-by-step between a range of amplitude. The amplitude and the rate of each slight change of luminosity is designated such that the pupils of one's eyes can obtain gentle exercise and yet the person is without knowledge that there is a luminosity change. A device like this thus is able to take care of one's health of eyes either mentally or physically.
The structure of human eyes is like a camera, and their operations in receiving the light and developing the image are similar too. While taking a picture, a camera must control the aperture ring, focus the distance-setting ring and develop the image at the film. The eyes of a human being operate likewise in response to light reflected to the eyes from an object or scene, it operates. The iris of the eye performs like the aperture ring at a camera. The crystalline lens operates as a camera lens operates. The pupil, which is the opened portion of the lens, is accommodated by the iris. And the retina of the eye can be compared to the camera's film. Therefore, whenever there is a change of luminosity, the pupil of the eye will enlarge or shrink so as to accommodate a suitable luminous flux. The accommodated range of the iris is so broad that it can accept a luminosity flux between 0.2 lx and 10.sup.5 lx. Due to the after-image visual effect, a slight change of luminosity of an image at the reting won't be perceived. If the luminosity changes in a small range over a time period, the eyes will recognize it as a stable average luminosity. Therefore, as long as the luminosity is changing at a small rate, people won't feel it. However, the pupils will sense and follow that change automatically. Thus a gentle accommodation is derived and a healthy lighting is obtained.
The existing modulation device for a lighting facility, whether a simple ON-OFF switch, a step-switch or a continuous modulation apparatus, once operated remains at that luminosity till otherwise being operated again. The pupils, under these kinds of control must respond in, an instant (and a very short period after) to the change of luminosity. This makes the eyes stay in a steady condition, with a constant level of tension of the eyes muscles. By contrast, there are other light modulation devices, such as one used for a glittering commercial board which purposely modulates the light in swiftly changes that attract our attention. A change of this kind over-excites the eyes.
In fact, good vision and comfortable light environment require enough illumination of the lighted object, a soft brightness contrast between the lighted object and its surrounding, a proper time duration of watching, and a proper change of luminosity at the light source. In other words, a change of luminosity will have the pupil accommodate accordingly. And to appropriately exercise and accommodate the muscles of the eyes, not to keep the eyes stay at a fixed tension over a long period, are the most effective ways of taking care of vision and, physical health, and of providing a happier atmosphere and a higher working efficiency. And yet, in order not to over-exercise or over-excite the eyes, the so-called luminosity modulation shall proceed in a gentle process that the eyes are able to accommodate.